Table 2 Quantification of aromatic moieties (lignin, hydroxycinnamates, inter-unit bondages) by combination analysis of ¹³ C and HSQC NMR spectra of wheat straw isolated MSL and CEL

Lignin aromatic units

Syringyl (S)

103.9/6.7 (S2/6),

25.7

27.3

24.1

24.5

106.4/7.4 (S'2/6 with α oxidization)

Guaiacyl (G)

110.8/6.97 (G2)

41.2

39.3

41.6

39.8

115.0/6.94 (G5),118.9/6.81 (G6)

p-hydroxyphenyl (H)

127.7/7.21 (H2/6)

1.6

1.4

2.3

1.8

S/G ratio

0.63

0.69

0.58

0.61

Hydroxycinnamates

p-benzoate (PB)

132.4/7.63 (PB2/6)

0.5

1.2

1.3

0.2

p-coumarate (pCA)

130.0/7.47 (pCA2/6),115.5/6.79 (pCA3/5)

5.4

5.5

3.0

3.1

144.74/7.47

Ferulate (FA)

110.9/7.32 (FA2), 122.5/7.15 (FA6)

0.6

6.4

0.4

4.5

p-coumarate/ferulate

9

0.86

7

0.68

Cinnamates/lignin and tricin

0.09

0.18

0.06

0.11

Lignin-ending group

Cinnamyl aldehyde (X2)

153.5/7.62 (X2α), 126.2/6.78 (X2β)

0.1

ND

ND

ND

Cinnamyl alcohol (X1)

128.34/6.44 (X1α), 128.35/6.22 (X1β)

0.6

ND

ND

ND

Lignan

Tricin (T)

104.04/7.30 (T 2′/6'), 104.65/7.03 (T3)

8.5

5.6

12

6.6

94.1/6.56 (T8), 98.8/6.22 (T6)

Inter-unit bondages

α-OH/β-O-4

71.1/4.74 (Aα-G), 71.8/4.8 (Aα-S)

28.3

33.8

31.7

36.5

α-keto/β-O-4

82.7/5.1 (Aα-keto)

1.5

2.4

0.4

1.1

Total β-O-4

29.8

36.2

32.1

37.6

Phenylcoumaran (β-5)

85.9/5.5 (Bα), 53.0/3.4 (Bβ)

5.4

5.7

3.0

4.1

Pino/resinol (β-β')

84.8/4.7 (Cα), 53.5/3.1 (Cβ),

1.3

0.9

1.4

1.2

Dibenzodioxocin (D)

83.4/4.9 (Dα), 85.5/3.8 (Dβ)

0.3

2.0

0.7

2.5

Spirodienone (SD)

81.4/5.0 (SDα), 59.5/2.8 (SDβ)

0.4

ND

ND

ND

α,β-diaryl ether (F)

79.6/5.5 (Fα)

0.5

2.1

0.4

1.3

γ-ending groups

γ-OH in X1 structure

62-58/3.8-3.0

2.0

1.5

1.2

0.9

Acylation on γ position

60.8-58.8/3.8-3.35

5.4

15.6

2.0

10.1